1. Field
This disclosure relates generally to use of microelectromechanical systems, and more specifically, to recovering from stiction events in MEMS devices through the use of an applied force orthogonal to a stiction force.
2. Related Art
Microelectromechanical systems (MEMS) devices are devices that provide moving parts with features having dimensions below 100 μm. These moving parts are formed using micro-fabrication techniques. MEMS devices have holes, cavities, channels, cantilevers, membranes, and the like. These devices are typically based on silicon materials and use a variety of techniques to form the proper physical structures and to free the mechanical structures for movement.
Stiction is a static friction force that is a recurrent problem with typical MEMS devices. While any solid objects pressing against each other without sliding require some threshold of force (stiction) to overcome static cohesion, mechanisms generating this force are different for MEMS devices. When two surfaces with areas below the micrometer range come into close proximity, the surfaces may adhere together due to electrostatic and/or Van der Waals forces. Stiction forces at this scale can also be associated with hydrogen bonding or residual contamination on the surfaces.
For MEMS devices such as accelerometers, surfaces such as over-travel stops come into close proximity or contact during use at the limits of the device design. In those situations, stiction forces can cause the MEMS device parts (e.g., a teeter-totter accelerometer mechanism) to freeze in place and become unusable. Traditional methods of avoiding such close proximity travel or contact include increasing spring constants and increasing distance between parts of the MEMS device. But avoiding stiction in this manner can decrease sensitivity of the device, and therefore decrease the utility of the MEMS device. It is therefore desirable to provide a mechanism for recovering from stiction-related interactions of MEMS devices without also decreasing sensitivity of the MEMS device.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.